1. Field of the Invention
The present invention relates generally to calibration and measuring devices. More particularly, the invention relates to a novel multipurpose instrument for use in checking and calibrating a wide variety of tools and measuring devies of the type commonly used in the lens manufacturing industry.
2. Discussion of the Prior Art
Tools and measuring devices commonly used in the business of lens manufacturing include lens clocks, lens meters, calipers, surfacing laps, and lens marking devices.
The lens clock is an instrument for determining the degree of curvature of a lens. It is usually a handheld device having somewhat the appearance of a clock or watch. Typically, the instrument is provided at one edge with three spaced apart feet which impinge the surface of the lens. These feet are movable in and out relative to the body of the instrument and sense the curvature of the lens. The face of the instrument is calibrated in diopters usually giving positive readings in a clockwise direction and negative readings in a counterclockwise direction in response to relative movement of the lens engaging feet.
Lens clocks are typically fragile and quite susceptible to damage if dropped or jarred. Prior to use, therefore, they must be routinely checked against a master standard. In the past, the standards used generally consisted of individual lens of supposedly known curvature. In practice these "standards" frequently consisted of ordinary lenses of standard manufacture and their curvature was taken to be that specified by the manufacturer of the lenses. This practice often led to gross inaccuracies in calibration. For example, depending upon the particular manufacturer and his particular manner of compensating to accommodate for error in the index of retraction of glass, a lens slated to be plus 8.00 diopters could well be plus 8.13 or even 8.25 diopters. Even when true individual master lenses were used by the lens maker, however, calibration errors were frequent because of damage to the master lens due to mishandling and wear.
These drawbacks of prior art practice in checking and calibrating lens clocks are effectively avoided through use of the instrument of the present invention. Each lens of the device of the present invention is precisely manufactured to exactly the stated curvature. Additionally, each lens is securely mounted with a sturdy gauge body to preclude damage. Further, the instrument embodies within the single gauge body a complete master lens set including lenses of plus 6.00 diopters, plus 12.00 diopters, minus 6.00 dopters, -12.00 diopters and a plano surface. This enables expeditious check and cross-check of the lens clock against each of the lenses of known, varying curvature, thereby virtually eliminating the possibility of calibration error.
The lens meter is an instrument designed for the measurement of the optical characteristics of spectacle lenses. Although commercially available lens meters vary somewhat in design, they typically embody a lens table or lens positioning ruler for supporting the lens and means for adjusting the table so as to center the lens within the instrument. Generally the lens meter also includes lens marking means for marking the center of the lens. Typically, the marking means comprises three spaced apart marker nibs movable into engagement with the specimen lens. One of these marker nibs generally indicates the center and the other two a particular axis or direction.
It is extremely important to periodically check the lens meter to make certain that the table is properly aligned and to calibrate the centering and vertical and horizontal axis indicators of the instrument. Additionally, periodic checks must be made of the lens marking means of the device to verify that accurate markings are being made on the specimen lenses.
In a manner presently to be described in greater detail, the unique design of the instrument of the present invention enables complete checking and calibration of all aspects of the lens meter apparatus. The alignment means of the instrument permits quick checking of the alignment of the lens meter lens table and the operably correlated indicia marking provided on the plano surface of the device enables expeditious checking and calibration of the vertical and horizontal axis indicators of the apparatus. The indicia marking on the plano surface also provide means for quickly and positively determining the accuracy of the lens marking means of the apparatus. Finally, the master lenses of the instrument provide ready means for precisely checking the diopter (powder) readings of the lens meter.
In addition, as will become apparent from the detailed description of the invention which follows, the instrument of the invention provides built-in easy-to-use means for readily checking and calibrating standard base curve gauges, thickness gauges, and calipers.